The present invention concerns a method for manufacturing an alkenyl group-containing organopolysiloxane.
There are conventionally known organopolysiloxanes, which contain alkenyl groups in the molecule, as in the case of dimethylpolysiloxane. For example, Walter Noll notes an alkenyl group-containing (e.g., vinyl group, etc.) organopolysiloxane in Chemistry and Technology of Silicones (Academic Press, 1968).
It is a well-established fact that an organopolysiloxane that contains an alkenyl group containing 3 or fewer carbon atoms can be copolymerized under conditions identical to those for polymerizing dimethylpolysiloxane. For example, a methylvinylsiloxane tetramer and dimethylsiloxane tetramer can be copolymerized in a nitrogen atmosphere in the presence of a potassium hydroxide catalyst at 120 to 170.degree. C. for 4 to 8 hours. The resulting siloxane copolymer can also be manufactured in the presence of an acidic clay catalyst in a nitrogen atmosphere at 70 to 110.degree. C. for 10 to 30 hours. It is also a well-established fact that an organopolysiloxane that contains an alkenyl group containing 4 or more carbon atoms, and which is characterized by a viscosity of 310 centistokes (cst) or above at 25.degree. C. can be copolymerized in the air in the presence of an alkali catalyst; see Japanese Kokai Patent No. Sho 62(1987)-86061.
It was discovered that, if an organopolysiloxane that contains an alkenyl group containing 4 or more carbon atoms is copolymerized using an alkali catalyst (e.g., potassium hydroxide, etc.) in a nitrogen atmosphere, gelation is induced. If said alkenyl group-containing organopolysiloxane is manufactured using an acidic catalyst (e.g., acidic clay, etc.), it is impossible to completely remove said acid catalyst from a high-viscosity product. Thus, the heat resistance deteriorates. It was also discovered that an organopolysiloxane that contains an alkenyl group containing 4 or more carbon atoms, and which is characterized by a viscosity of 300 cst or above at 25.degree. C. cannot be copolymerized in the air in the presence of an alkali catalyst.
The present inventors compiled exhaustive research to eliminate the aforementioned problems inherent to conventional methods. Thus, the present invention has been completed. The present invention, which has been proposed to eliminate the aforementioned problems, provides a method for manufacturing an alkenyl group-containing organopolysiloxane in which copolymerization can be quickly induced in the presence of an alkali catalyst, without inducing gelation.